It has been customary to employ a pump unit unitarily combining a pump section and a motor section in feeding liquid in piping lines. In such a pump unit, the pump section and the motor section are generally installed in a casing as a unit and, thus, the rotatable shaft thereof is not required to project through its casing. However, in assembly of such a unit it has been a problem to establish proper alignment of the impeller of the pump with respect to the pump casing thereby consuming many manhours. Also, to achieve the required alignment, the elements or components had to be made to strict tolerances.
Also, in order to prevent leakage of liquid from the pump section into the motor section, a mechanical seal has usually been employed where the rotational shaft extends through a pump casing. However, if failure occurs in the mechanical seal, liquid will leak from the seal and enter the motor section thereby creating the possibility of wetting the motor coil. To protect the motor section from such possibility, a drain ring has been installed on the shaft; however, the drain ring has not been satisfactory since it does not completely prevent the motor section from getting wet.
Also, the temperature of the motor and the motor unit is usually raised during use and, thus, air ventilation is essential in this type of pump unit. However, if efficiency of the ventilation is improved, it increases the chance that rain or water may easily get inside the motor section and cause malfunction of the motor. Further, a pump casing having an inlet port and an outlet port and a volute casing to be disposed within the pump casing have been unitarily produced by casting process; however, the casting process has been relatively difficult due to the complicated structure of the casings. Also, in order to effect complete sealing of the casing, it has been necessary to dispose a seal member on top of the casing between the pump casing and the upper wall covering the casing.
Accordingly, it has been desired to obviate the drawbacks above in the pump unit of the prior art.